By Stephanie Apstein The American became the first Black woman to win an individual gold medal at the Winter Olympics. BEIJING — Erin Jackson is never happier than when she is thinking. She holds two degrees and is on her way to a third. Her family lovingly calls her a nerd. She sometimes refers to her job—at which, on Sunday night, she was crowned best in the world—as “skating in circles.” It was not surprising that she won the 500-meter speedskating event in 37.04 seconds, becoming the first Black woman to win an individual gold medal at the Winter Olympics and the first American woman to wi…